Re: pg_stat_bgwriter.buffers_backend is pretty meaningless (and more?)

Tom Lane <tgl@sss.pgh.pa.us>

From: Tom Lane <tgl@sss.pgh.pa.us>

To: Andres Freund <andres@anarazel.de>

Cc: Kyotaro Horiguchi <horikyota.ntt@gmail.com>, melanieplageman@gmail.com, vignesh21@gmail.com, pryzby@telsasoft.com, lukas@fittl.com, alvherre@alvh.no-ip.org, magnus@hagander.net, pgsql-hackers@postgresql.org, thomas.munro@gmail.com, m.sakrejda@gmail.com

Date: 2023-03-04T23:21:09Z

Lists: pgsql-hackers

Andres Freund <andres@anarazel.de> writes:
> Just pushed the actual pg_stat_io view, the splitting of the tablespace test,
> and the pg_stat_io tests.

One of the test cases is flapping a bit:

diff -U3 /home/pg/build-farm-15/buildroot/HEAD/pgsql.build/src/test/regress/expected/stats.out /home/pg/build-farm-15/buildroot/HEAD/pgsql.build/src/test/regress/results/stats.out
--- /home/pg/build-farm-15/buildroot/HEAD/pgsql.build/src/test/regress/expected/stats.out	2023-03-04 21:30:05.891579466 +0100
+++ /home/pg/build-farm-15/buildroot/HEAD/pgsql.build/src/test/regress/results/stats.out	2023-03-04 21:34:26.745552661 +0100
@@ -1201,7 +1201,7 @@
 SELECT :io_sum_shared_after_reads > :io_sum_shared_before_reads;
  ?column? 
 ----------
- t
+ f
 (1 row)
 
 DROP TABLE test_io_shared;

There are two instances of this today [1][2], and I've seen it before
but failed to note down where.

			regards, tom lane

[1] https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=grison&dt=2023-03-04%2021%3A19%3A39
[2] https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=mule&dt=2023-03-04%2020%3A30%3A05

Commits

Stabilize pg_stat_io writes test
- ef719e7b32fc 16.0 landed
Fix flakey pg_stat_io test
- 1be0fdb9de55 16.0 landed
Suppress more compiler warnings in new pgstats code.
- b1b86820d84e 16.0 landed
Suppress compiler warnings in new pgstats code.
- 728560db7d86 16.0 landed
Add tests for pg_stat_io
- 10a082bf7215 16.0 landed
Create regress_tblspc in test_setup
- 9c83bbcf7ef6 16.0 landed
Add pg_stat_io view, providing more detailed IO statistics
- a9c70b46dbe1 16.0 landed
pgstat: Track more detailed relation IO statistics
- f30d62c2fc60 16.0 landed
pgstat: Infrastructure for more detailed IO statistics
- 28e626bde00e 16.0 landed
doc: Fix some issues in logical replication section
- 4f74f5641d53 16.0 cited
Manual cleanup and pgindent of pgstat and bufmgr related code
- 250c8ee07ede 16.0 landed
Have the planner consider Incremental Sort for DISTINCT
- 3c6fc58209f2 16.0 cited
Use actual backend IDs in pg_stat_get_backend_idset() and friends.
- d7e39d72ca1c 16.0 cited
Remove redundant call to pgstat_report_wal()
- 1bdd54e662d5 16.0 landed
Add BackendType for standalone backends
- 0c679464a837 16.0 landed
Initialize backend status reporting during bootstrap.
- 3b34645678d1 15.0 landed